Mini FKmr and FTn3Kmr plasmids are being mapped for the location of replication, copy number control, incompatibility and segregation genes. The methods used employ chemical mutagenesis, insertional mutagenesis by acquisition of the ampicillin resistance transposon Tn3, Tn3 induced deletions, and in vitro recombination. The phenotypic consequences of these genetic manipulations are being examined with special emphasis on copy number control and its relationship to plasmid incompatibility.